Many types of ganglion cell are not electrically isolated, but are coupled to neighboring ganglion cells of the same type and/or to amacrine cells. These networks almost certainly alter their coupling properties as the retina adapts to changing backgrounds and are likely to promote oscillations and response synchrony when well coupled, and perhaps employ complex mixed chemical/electrical signalling. This proposal will use quantitative modeling techniques developed by the PI to identify the specific cells in these circuits and test specific hypotheses about the anatomical and pharmacological details that determine their coupling properties. It will also identify currently unknown cell types that use the gap junctional protein connexin36. Specific Aim 1: OFF alpha ganglion cells will be injected with Neurobiotin. The relative distribution of tracer in the coupled network will be measured under different neuromodulatory conditions. The results will reveal which cells are directly coupled, what dopamine receptor types are present on each cell type, and how the gap junctions are controlled by the combination of receptors and kinases in different portions of the circuit. Specific Aim 2: Amacrine cells that are electrically coupled to ganglion cells will be stained by retrograde transport of tracers. They will be identified by direct injection of dye. Modulation of these gap junctions by light/dopamine analogs will indicate when coupling is most active. All ganglion cell types that participate in these coupled networks will be identified and matched up with their amacrine cell components. Specific Aim 3: Cells expressing connexin36 appear in sublamina a, but are unidentified. The PI will determine whether these are OFF cone bipolar cells and/or OFF alpha ganglion cells, both known to be tracer-coupled. He will also test the gating and fundamental permeability of connexin36 channels in retina and an expression system to determine if these channels have the same permeability to tracers and gating behavior at all locations. He will determine if phosphorylation alters the permeability of individual connexin36 channels, or only changes the probability that they are open to a single state permeant to tracer.